The statements in this section merely provide background information related to this disclosure and may not constitute prior art.
Industrial coating of metal articles that will be used in corrosive environments may include application of one or more inorganic and organic treatments and coatings. Painting systems (“paint shops”) in automotive assembly plants are large, complex, and expensive. Metal automotive vehicle bodies (the “body-in-white”) and parts, for instance, are given a many-step treatment of cleaning in one or more cleaning baths or spray tanks, application of an aqueous phosphate coating material as a metal pretreatment step in a phosphating bath, then various rinses and additional finishing treatments, such as described in Claffey, U.S. Pat. No. 5,868,820. The phosphating pre-treatment steps are undertaken to improve corrosion resistance of the metal and adhesion of subsequent coatings to the metal. The cleaning and phosphating steps may have 10 or 12 individual treatment stations of spray equipment or dip tanks.
An electrodeposition coating (“electrocoat”) is applied after the pretreatment steps to the metal vehicle body. Electrocoat baths usually comprise an aqueous dispersion or emulsion of a principal film-forming resin (“polymer” and “resin” are used interchangeably in this disclosure), having ionic stabilization in water or a mixture of water and organic cosolvent. In automotive or industrial applications for which durable electrocoat films are desired, the electrocoat compositions are formulated to be curable (thermosetting) compositions. This is usually accomplished by emulsifying with the principal film-forming resin a crosslinking agent that can react with functional groups on the principal resin under appropriate conditions, such as with the application of heat, and so cure the coating. During electrodeposition, coating material containing the ionically-charged resin having a relatively low molecular weight is deposited onto a conductive substrate by submerging the substrate in the electrocoat bath and then applying an electrical potential between the substrate and a pole of opposite charge, for example, a stainless steel electrode. The charged coating material migrates to and deposits on the conductive substrate. The coated substrate is then heated to cure or crosslink the coating.
One of the advantages of electrocoat compositions and processes is that the applied coating composition forms a uniform and contiguous layer over a variety of metallic substrates regardless of shape or configuration. This is especially advantageous when the coating is applied as an anticorrosive coating onto a substrate having an irregular surface, such as a motor vehicle body. The even, continuous coating layer over all portions of the metallic substrate provides maximum anticorrosion effectiveness. The phosphate pre-treatment, however, has up to now been an indispensable step in protecting against corrosion for automotive vehicle bodies.
Benson et al., U.S. Pat. No. 7,342,082 discloses a thermoset system of polymers having pendant acylsulfonamide groups that can be used as an amine capture agent, e.g., for to immobilize analytes, amino acids, DNA and RNA fragments, organelles, or immunoglobins on a surface. Wear, U.S. Pat. No. 3,110,701 discloses a thermosetting composition containing poly(benzosulfimido) group-containing compounds and polyfunctional primary aliphatic amines that can be applied to fabrics and other materials of organic character, such as clot-insulated wire or to metals to provide tough, adherent uniform coatings with excellent resistance to corrosion. A copolymer of poly(benzosulfimido) group-containing compounds and polyfunctional primary aliphatic amines is disclosed. The poly(benzosulfimido) group-containing compounds are formed by polyhalo compounds and sodium salt of saccharin.